Porous filter media support plate

ABSTRACT

Disclosed is a porous filter support plate of the kind used in traveling bridge filters for the support of granular filter media used in the filtration of waste water, industrial liquors or baths, or for filtration of potable water in a water purification system. The support plates are formed of porous, heat-fusible materials, for example, a thermoplastic organic material, joined together by heat-fused butt joints and/or reinforced by vertical zones which extend vertically through the plates in which the material has been brought to a molten state and is pressed together to form a dense, solid, non-porous mass.

FIELD OF THE INVENTION

This invention relates to porous filter support plates, usefulparticularly for traveling bridge filters or the like for the filtrationof waste water or industrial liquors or baths or for filtration ofpotable water as an adjunct to a water purification system.

BACKGROUND AND PRIOR ART

Filtration systems of the kind referred to are generally comprised of anumber of elongated, generally rectangular, filter cells or beds spacedin side-by-side relationship. Each cell contains a single granularfilter media, such as sand, or two kinds of media, such as sand andpulverized anthracite coal. Water to be filtered is delivered from aboveto flood the cells, the water flowing downwardly through the media bygravity leaving particulate matter entrapped in the spaces between themedia particles. The bed of filter material within each cell rests on asupport plate commonly called a drainplate which in the past was formedof a porous ceramic material. More recently, porous drainplates madefrom thermoplastic materials have been substituted for the drainplatesformed of ceramic materials. Amongst the advantages of such plasticplates are substantially reduced weight and material costs, lower laborand shipping costs, and simplified installation. The plates are toughand resilient and can be easily joined together. They can be made longerthan the ceramic plates thereby minimizing joints. They can be easilyhand-sawed for custom field fits where required.

In filtering equipment of the kind described, a traveling backwash hoodmounted over the cells moves from cell to cell and is used inconjunction with a pump to periodically backwash each cell and removeparticulate and other debris from the drainplate and the filtrationmedia. An advantage of this equipment is that while one cell is shutdown, others are in operation, thereby providing substantiallycontinuous filtration.

A problem with thermoplastic drainplates of the kind referred to is thatthey tend to bow or bend in planes extending transversely of theirlength under the combined loading of the filter media and the water.When overloaded, the sides of the plates pull away from the verticalsidewalls of the cells. This results in a channelling of the water downthe sides of the cells around the sides of the drainplates therebyreducing the efficiency of the filter and of the backflushingoperations.

SUMMARY AND OBJECTS OF THE INVENTION

According to the invention, porous drainplates of a heat-fusiblematerial are provided having longitudinally-spaced, relatively narrowheat-fused non-porous zones extending vertically through the plates andfrom one side edge to the other. Preferably these zones are formed bythe application of heat transversely of a solid porous plate to form anarrow heat-fused non-porous zone or by butt welding pieces inend-to-end relationship or by a combination of both methods. By eithermethod, these zones form rigid beams integrally with the porous platesto resist bending or bowing and substantially eliminate channeling ofthe water being treated around edges of the plates. As compared withpieces which have lap joints mastic bonded in end-to-end relationship ithas been found that the butt-welded pieces and the pieces havingtransversely-extending fused zones are approximately ten times asresistant to bending or bowing.

Accordingly, a primary objective of the invention is the provision ofheat-fused zones extending in vertical planes transversely throughporous heat-fusible drainplates.

A related objective of the invention is the treatment of such plates ina manner which imparts substantially more rigidity for a given platethickness than has been heretofore possible.

The foregoing and other objects of the invention are achieved in aporous drainplate, wherein the plate supports a bed of filter mediawithin each filtration cell wherein the plate has pores sized to retainthe filter media and solid particulate matter while permitting thepassage of filtered water downwardly through the filter media and theplate and the passage of washing water in the reverse direction firstthrough the plate and then through the filter media, wherein the plateis provided with at least one relatively narrow heat-fused non-porouszone consisting essentially of the material which comprises the plate,the heat-fused non-porous zone extending in a plane which passesvertically from the top to the bottom and from one side edge to theother of the plate.

In preferred form, the drainplate comprises a thermoplastic material,for example, an organic polymeric material.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, FIG. 1 shows in schematic form an elevational view of afiltration apparatus of the kind incorporating drainplates of thepresent invention;

FIG. 2 is a perspective view on an enlarged scale with respect to FIG.1, of a single filtration cell of the filtration apparatus shown in FIG.1;

FIG. 3 is a perspective view of a drainplate of the kind comprising thepresent invention; and

FIG. 4 is a detail sectional view taken on line 4--4 of the drainplateof FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made to FIG. 1 which shows in schematic form atypical filtration unit 10 incorporating the invention. In apurification system comprising the filtration unit 10, water containingsuspended solids is delivered through an influent pipe 11 to thefiltration unit schematically indicated by the reference character 12.The filtration unit comprises a rectangular tank containing a pluralityof relatively narrow cells 13 which are separated byvertically-extending partitions 14 which extend transversely from onetank sidewall to the other.

Fragments of such cells are shown in FIG. 2. Support means fordrainplates for the filter media, as described hereinafter, comprisehorizontally-extending flanges 15 which project inwardly from thebottoms of partitions 14 and extend lengthwise of each cell. Porousfilter media drainplates 16 to be described more particularlyhereinafter extend lengthwise of the cells and are supported on theflanges 15. These plates support the granular filter material whichtypically comprises a bed of sand shown at 17 and a bed of pulverizedanthracite coal 18 which rests upon the sand bed 17. A sealant bead notshown may be applied along the upper surface of supports 15 to effect aseal with the side wall along the edges of the plates. In addition, aretaining angle, a portion of which is shown at 19, is secured to eachwall 14 to hold plates 16 in place. The sealant should preferably alsobe applied along the upper perimeter of each plate so that a good sealis effected between the plate and the side walls.

Water to be filtered is delivered through the influent pipe 11 andfloods the upper surfaces of each of the cells 13. The water passesdownwardly through the beds by gravity leaving the suspended solidsbehind within the beds. The filtered water flows through the porousdrainplates 16 into an underdrain or clearwell 20. An effluent pipe 21is in liquid communication with the clearwell for discharge of filteredeffluent. A spillway or dam 20a intermediate the clearwell and theeffluent pipe 21 controls the level of water in the clearwell.

As is known in the art, a traveling backwash hood 22 which is carried bya horizontal movable carriage 23 periodically moves from cell to cell.The hood has a sealing strip around its lower perimeter which forms aseal with flange sealing surfaces 24 which extend around the perimeterof each cell and is also provided with a suction manifold, not shown.Once a seal is formed with the sealing surfaces 24, a backwash pump 25is activated to cause a flow upwardly through the cell, then through thehood 22 and outwardly through a backwash conduit 26. The backwashoperation, as described, purges each cell of suspended solids and otherdebris removed by the filter materials within the cell. The seal is thenbroken and the hood moved to the next cell, the arrangement providingsubstantially continuous operation through the cells not beingbackwashed and continuous periodic backwashing of all cells.

Cells of the type in which the drainplates of the invention are utilizedtypically have a width (w) of 7 to 12 inches or even more, a length (1)up to 16 feet or even more, and a thickness (t) of about one inch. Inthe past, porous thermoplastic plates formed of polyethylene have beenprovided either having a length as long as the cell or, if shorter andjoined together, are joined by a lap joint with the surfaces forming thejoint are glued together with a mastic sealant.

In carrying out the invention, the plates 16 are formed in known manner,for example, by sintering a heat-fusible particulate material, forexample, a thermoplastio, organic, material such as high-densitypolyethylene to the desired rectangular shape. Other heat-fusibleplastic materials such as polypropylene may be employed if desired. Theplates so formed are then provided with relatively narrow heat-fused,relatively dense, non-porous zones 30 as shown in FIG. 4, which zonesextend through the plates in vertical planes from the top surface to thebottom surface of each plate. Zones 30 are formed by application of heatto the ends of two pieces of the thermoplastic material while joiningthe ends together and then allowing the pieces to cool until thematerial solidifies and forms a rigid non-porous joint. Alternatively,where the fusion zones 30 are formed intermediate the ends of the plate,sufficient heat and pressure are applied to cause the material to reachthe melting point in a zone extending through the piece and from sideedge to side edge as by use of any suitable heating means represented bytransversely-movable electrical heating element 35 in FIG. 3. In effect,the zones are rigid, non-porous integrally formed beams having a depthof the thickness of the plate, which beams are effective to withstandthe bending forces supplied by the load of filter media.

The number of fusion zones for a particular application will varysomewhat depending on the dimensions of the drainplates and the loadingto which they are exposed and can be determined after a few field tries.The zones in a typical application may vary from about one every twofeet to one every four feet. As illustrated in FIG. 3, combinations ofzones formed by butt welding two plates together and forming zoneswithin a length of drainplate may be employed.

EXAMPLE

Porous media drainplates having a thickness of one inch, a width ofeight inches and a length of four feet are formed of a polymer comprisedof a high density polyethylene of molecular weight about 800,000 as soldby Phillips Plastics, product number M550. This material is provided inbead or pellet form, the pellet size being one-eighth of an inchdiameter. Pellets of the polymer of one-eighth of an inch diameter arejoined in known manner by heating in a rectangular mold to a temperatureof 360° F., at a pressure of about 700 psi, to form a rectangular porousplate having a weight of three pounds per square foot, a bulk density of38 to 40 pounds per cubic foot and a pore volume of 40% to about 55%.Such plates have a capability of retaining sand particles down to about0.45 mm in diameter. A melted zone is then formed by heating with afusion plate heater while the plates are held together. When thesurfaces are in a molten state the heater is removed and pressure isapplied to the plate ends by air cylinders until the molten polymerfills the pores within the zone and solidifies, resulting in a narrownon-porous zone or web.

Examples of other materials that can be used as resins in products madeaccording to the foregoing examples, and which have been found toperform satisfactorily are as follows:

(1) High density, high molecular weight polyethylene resin10571--containing 45% mica filler as supplied by the AmpacetCorporation;

(2) High density, high molecular weight polyethylene resin #10647containing 50% of a talc filler, as supplied by the Ampacet Corporation;

(3) A nylon resin type 6/12 as supplied by E. I. Dupont DeNemours & Co.;and

(4) A poly(vinyl chloride) resin Geon 8714 as supplied by the B. F.Goodrich Company.

I claim:
 1. An elongated substantially rectangular filter media supportplate comprised of a porous heat-fusible organic plastic material, saidplate being exposed to a loading by a porous filter media, the pores inthe support plate being sized to retain the filter media and wasteparticulate matter while permitting passage of water in a firstdirection first through the filter media and then through the supportplate and in the reverse direction first through the support plate andthen through the filter media, said plate comprising means forming atleast one relatively narrow, non-porous heat-fused zone extending acrossthe plate from one side edge to the other and from the upper surface tothe lower in a plane extending substantially perpendicularly to saidupper and lower surfaces and to said side edges, each said zonesub-dividing the plate into end-to-end abutting porous sub-sections,said plate being performed with each said heat-fused zone forming anintegral part of said plate with the composition of the material in thesaid zone being homogeneous with the material outside of the zone andforming within the zone a substantially rigid, load-bearing beamextending from said one side edge to the other and from the said uppersurface to the said lower surface.
 2. A support plate according to claim1 wherein said material is a high density polyethylene.
 3. An elongatedsubstantially rectangular filter media support plate comprised of aporous heat-fusible organic plastic material, said plate being exposedto loading by a porous filter media, the pores in said support platebeing sized to retain the filter media and waste particulate matterwhile permitting passage of water in a first direction first through thefilter media and then through the support plate and in the reversedirection first through the support plate and then through the filtermedia, said plate comprising a plurality of narrow, non-porousheat-fused zones extending from one side edge to the other and from theupper surface to the lower in planes extending substantiallyperpendicularly to said upper and lower plate surfaces and to said sideedges, said heat-fused zones sub-dividing the plate into end-to-endabutting porous sub-sections, each of said heat-fused zones integrallyjoining the abutting ends of the porous sub-sections.
 4. A support plateaccording to claim 3 wherein said material is a high densitypolyethylene.